🏷️ Basic Information

Make:

Mercedes-Benz

Model:

S-Class

Chassis Code:

W140

Coupe Chassis Code:

C140

Model Year:

1991

👋 Introduction

Market Position:

The 1991 Mercedes-Benz S-Class (W140) represented the pinnacle of automotive luxury and engineering for its era, setting new benchmarks in safety, comfort, and performance. This manual targets owners and independent repair professionals seeking the most accurate and detailed information for maintaining and repairing these sophisticated vehicles.

Competitive Analysis:

At its launch, the W140 S-Class competed with other flagship luxury sedans from brands like BMW (7 Series), Lexus (LS 400), and Audi (V8 Quattro). Its advanced technology, build quality, and extensive features positioned it as a segment leader. This factory manual is superior to generic repair guides due to its vehicle-specific detail.

Key Features:

Vehicle-specific repair data, factory diagrams and schematics, comprehensive A-Z coverage, digital convenience, printable pages, high detail for accurate diagnostics and repairs.

Target Audience:

DIY enthusiasts, independent Mercedes-Benz specialists, and professional automotive technicians.

Value Proposition:

This manual offers significant value by providing the exact, manufacturer-authorized information needed to perform accurate and efficient repairs, saving time and money compared to relying on generic guides or trial-and-error diagnostics.

📋 Manual Details

Coverage Areas:

All models and all repairs A-Z for 1991 Mercedes-Benz S-Class (W140) and Coupe (C140)

Page Count:

Not specified, but described as a complete manual with extensive coverage.

Manual Type:

Service and Repair Manual (Factory Technical Documentation)

Language:

English

Format:

PDF (digital)

Format Features:

Searchable text, ability to zoom into diagrams and illustrations, print selected pages or entire sections for convenient workshop use.

📖 Manual Coverage

Systems Covered:

Engine, Control System, Mechanical, Fuel Service Specifications, Emission Control, Intake, Exhaust, Cooling, Lube, Ignition, Starting, Charging, Auto Transmission, Clutch, Manual Transmission, Transfer Propeller Shaft, Drive Shaft, Differential, Axle, Suspension, Tire & Wheel, Brake Control, Brake, Parking Brake, Steering Column, Power Steering, Air Condition, Suppl. Restraint System, Seat Belt, Engine Immobilizer, Cruise Control, Wiper & Washer, Door Lock, Meter, Audio/Visual, Horn, Windshield/Glass Mirror, Instrument Panel, Seat, Engine Hood/Door, Exterior & Interior, Electrical, Multiplex/CAN Communication.

Procedures Included:

Maintenance, Service, Diagnosis, Repair, Troubleshooting, Component Replacement, Adjustments, Specifications, Wiring Schematics, Diagrams, Illustrations.

Technical Depth:

Factory highly detailed, comprehensive step-by-step instructions, covering everything from basic maintenance to complete vehicle repair. Exact same information used by dealership technicians.

Engine Mechanical:

Complete engine overhaul procedures, including cylinder head removal/installation, piston and connecting rod service, crankshaft and bearing inspection, camshaft timing, and valve train adjustments.

Engine Electrical:

Detailed ignition system diagnosis (ECU, coil packs, spark plug wires), starting and charging system analysis (starter motor, alternator, battery), and sensor testing (e.g., crankshaft position sensor, camshaft position sensor).

Fuel System Diagnosis:

Troubleshooting fuel delivery issues, diagnosing fuel pressure problems, and testing fuel injectors and fuel pump operation.

Cooling System:

Radiator, water pump, thermostat, coolant hoses, and cooling fan system inspection, removal, installation, and leak testing.

Transmission Overhaul:

Step-by-step instructions for complete automatic transmission disassembly, cleaning, inspection of internal components (clutches, seals, valve body), and reassembly.

Brake System:

Front and rear brake caliper service, rotor replacement, brake pad inspection and replacement, brake fluid bleeding procedures, and ABS system component diagnostics.

Suspension Steering:

Inspection and replacement of ball joints, tie rod ends, control arms, shock absorbers, springs, and power steering system components (pump, rack and pinion, hoses).

Electrical Schematics:

Comprehensive wiring diagrams for all vehicle systems, allowing for accurate tracing of electrical circuits and troubleshooting of faults.

Body And Trim:

Procedures for removing and installing interior and exterior trim, door panels, bumpers, fenders, and hood.

Climate Control:

Diagnosis and repair of the automatic climate control system, including refrigerant handling, compressor service, evaporator and heater core replacement, and sensor troubleshooting.

Diagnostic Trouble Codes:

While not explicitly stated, factory manuals typically include procedures for retrieving and interpreting Diagnostic Trouble Codes (DTCs) from various control modules.

Emission Control Systems:

Detailed information on emission control components such as the catalytic converter, oxygen sensors, EGR system (if applicable), and evaporative emission control system.

Lighting System:

Headlight, taillight, interior lighting, and auxiliary lighting system diagnosis and repair, including bulb replacement and wiring checks.

Wiper Washer System:

Service and repair of the windshield wiper motor, linkage, blades, washer pump, and fluid reservoir.

Power Accessories:

Diagnosis and repair of power windows, power seats, power mirrors, power door locks, and remote central locking systems.

Safety Restraint System:

Detailed coverage of the Supplemental Restraint System (SRS), including airbag module diagnostics, occupant sensors, and seat belt pre-tensioners.

Cruise Control System:

Troubleshooting and repair procedures for the cruise control system, including the control module, actuators, and speed sensors.

Instrument Panel Gauges:

Diagnostic procedures for the speedometer, tachometer, fuel gauge, coolant temperature gauge, and warning indicator lights.

Door And Lock Mechanisms:

Repair and adjustment of door latches, hinges, window regulators, and central locking actuators.

📊 Manual Specifications

File Format:

PDF

Print Quality:

Printable, with ability to blow up images and print enlarged copies.

Binding Type:

N/A (Digital Download - no physical binding)

Paper Type:

N/A (Digital Download - printable to any paper type)

File Format Compatibility:

Compatible with Windows Vista (32 and 64), XP, ME, 98, NT, 2000, and MAC operating systems.

Software Requirements:

Requires Adobe PDF Reader and WinZip (or equivalent decompression software), both available for free online.

Searchability:

The PDF format allows for full-text searching, enabling users to quickly locate specific procedures or components.

⚙️ Engine Specifications

Primary Engine:

While the product information doesn't specify engine variants for 1991, the W140 typically offered V8 (M119) and V12 (M120) engines. This manual would cover all available engines for the 1991 model year.

Performance:

The manual provides detailed specifications for engine performance parameters, including horsepower, torque, and operational limits.

Fuel System:

Comprehensive coverage of fuel injection systems (likely Bosch KE-Jetronic or similar), fuel pumps, injectors, fuel pressure regulators, and emissions control related to the fuel system.

Engine Codes:

The manual would cover specific Mercedes-Benz engine codes relevant to the 1991 W140, such as M119 (4.2L, 5.0L V8) and potentially M120 (6.0L V12) if equipped.

🔧 Transmission

Standard:

Likely a 4-speed automatic transmission (e.g., 722.3 or 722.4) for most models, with potential for a 5-speed automatic on later variants or specific engines.

Optional:

While less common for the early W140, manual transmissions were not typically offered in the S-Class. The manual details automatic transmission service, diagnosis, and repair.

Features:

Detailed procedures for transmission fluid changes, filter replacement, internal component diagnosis, shift control, and electronic transmission control unit (ETC) troubleshooting.

Gear Ratios:

Specific gear ratios for the automatic transmission models covered are detailed within the manual for performance and diagnostic purposes.

📐 Dimensions

Exterior:

The manual includes specifications for vehicle dimensions relevant to bodywork, panel alignment, and component replacement.

Interior:

Information related to interior component removal and installation, such as dashboard, seats, and trim panels.

Weights:

Curb weights and Gross Vehicle Weight Ratings (GVWR) are likely included, crucial for suspension and brake servicing.

Wheelbase:

Standard wheelbase for W140 sedan: 118.5 inches (3010 mm). Long wheelbase: 121.3 inches (3081 mm). C140 Coupe wheelbase: 112.6 inches (2860 mm).

Wheel Bolt Pattern:

Typically 5x112mm for Mercedes-Benz vehicles of this era.

🛡️ Safety Features

Ratings:

While specific crash test ratings for 1991 models might be less prominent in this era's manuals, the manual details the Supplemental Restraint System (SRS) components, including airbags and seat belt pretensioners, and their diagnostic procedures.

Active Features:

Covers systems like ABS (Anti-lock Braking System), Traction Control (ASR - Acceleration Slip Regulation), and self-leveling suspension, detailing their operation and repair.

Passive Features:

Detailed procedures for airbag system diagnosis, seat belt mechanisms, and structural component repair.

💡 Technology Features

Infotainment:

Details on the audio system, climate control system, and instrument cluster diagnostics and repair procedures.

Driver Assistance:

Coverage of ABS, ASR (Traction Control), and potentially early forms of adaptive cruise control or electronic stability control depending on the specific 1991 configuration.

Connectivity:

Includes information on the vehicle's Multiplex/CAN Communication system, essential for diagnosing electronic module interactions and wiring faults.

Infotainment Features:

This manual provides diagnostic and repair procedures for the factory radio, cassette player, and potentially a CD changer, as well as the climate control display and controls.

🔧 Maintenance

Service Intervals:

The manual provides detailed factory-recommended service intervals for all major maintenance tasks, including oil changes, filter replacements, fluid checks, and belt inspections.

Fluid Specifications:

Specific part numbers and types for engine oil (e.g., MB 229.1 compliant), coolant, brake fluid (e.g., DOT 4), power steering fluid, and automatic transmission fluid (e.g., MB 236.81 or similar).

Known Issues:

While not explicitly listed as 'common issues,' the detailed diagnostic procedures within the manual would implicitly guide technicians to address common W140 concerns such as vacuum-actuated systems, wiring harness degradation, climate control issues, and ignition system components.

Oil Capacity:

Engine oil capacity varies by engine, but typically around 7.5-8.5 liters for V8 engines and potentially more for V12 engines, requiring specific Mercedes-Benz approved oil grades.

Coolant Capacity:

Coolant capacity is approximately 10-12 liters, requiring a specific Mercedes-Benz approved coolant (e.g., G48).

Tire Sizes:

Commonly 215/60R15 or 235/60R15 for standard models, with larger sizes available for sportier variants or optional wheels.

📚 Vehicle History

Brand Heritage:

Mercedes-Benz has a long-standing reputation for engineering excellence, luxury, and durability, with the S-Class lineage representing the flagship sedan for decades, embodying technological innovation and comfort.

Model Evolution:

The W140 generation, introduced in 1991, was a significant redesign from its predecessor (W126), growing in size and complexity, and introducing technologies like dual-pane windows, CAN bus communication, and more advanced electronic systems.

Production:

The W140 was produced from 1991 to 1998. This manual specifically covers the early part of this production run.